Bags

iTrader: (3)

I am trying to get more info on our fuel system...

so from my understanding a FMU rasies fuel pressure according to boost....

for example a 12:1 FMU rasies fuel pressure 12 PSI for every pound of boost.


Ok, so how many PSI should our fuel system see?

How much PSI can our stock FPR handle?

At idle what should the Fuel Flow PSI be?

What is our injector limit in CC?

What is our injector limit in PSI?

If there is something I am missing PLEASE fill it in

Ramius83

On stock injectors, no more than 110 psi. I would say that you need to stick around 90 psi tops.

It can handle any amount, but with the Walbro fuel pump, the idle and WOT Fuel pressure is changed.

Idle should be at 32 psi or so and WOT should be around 42-44 psi.

I think around 240-290CC

110 psi


If I were you, I would drop the disk down to atleast a 10:1. That right there should do you well for now until you get your system fully tuned out. And even if you are planning on getting a S-AFC or identical fuel unit, the 10:1 is the way to go.

[maxi-overdose]

iTrader: (3)

fuel pressure @ boost = amount of boost * FMU ratio + half of your idle fuel pressure.


so...10 psi with an 8:1 FMU and my idle pressure is 40psi

I will get
10*8 + 40/2 = 100psi.

I do see over 100psi on my fuel pressure gauge. 8:1 is enough for everybody here. I even thought to drop it down to 6:1 to lean her out a bit.

BigDogJonx

iTrader: (7)

Kirk, if you plan on staying at 5psi for awhile, then for sure 6:1 is going to be more than enough. If you plan on pushing it to 10psi, I will say 8:1 is still fine.

You might as well purchase the entire disc kit from vortechsuperchargers.com Its like $44 Comes with 4:1, 6:1, 8:1, 10:1, 12:1 discs.

Bags

iTrader: (3)

Thanks erik your my hero again..lol

maxi-overdose- thanks for the formula, give a man a fish feed him for a day... you know the rest

dixit- yeah I rememeber you saying that I will call you either tommorow or friday, but if possible I would like to come by sunday

[maxi-overdose]

iTrader: (3)

no problem...

question to everyone....if you are boosting at 1psi, does this formula still apply? if so, boosting at 1 psi actually = 28psi of fuel pressure. boosting @ 2 psi is still low: 36psi of fuel p.

Stephen Max

iTrader: (59)

Since the fmu is in series with the fpr, whichever is set for the higher pressure is the one that controls the fuel pressure. So at 1 psi, if the fpr is set at 43 psi for instance, and the fmu is set at 28 psi, then your fuel pressure is going to be 43 psi. Once the boost pressure gets high enough to where the fmu is producing 43 psi, then it starts to control the fuel pressure.

[maxi-overdose]

iTrader: (3)

thx Stephen!

so at low boost, fpr overwrites the fmu and vice versa @ high boost.

Y2KevSE

iTrader: (13)

Yes, I have an extra disc but it is more cost effective to buy the whole kit so you don't have to purchase multiple discs.

Bags

iTrader: (3)

ok I will go that route.. but I might need to still buy somethign from ya...lol

nismology

iTrader: (8)

Sorry to bring back this old thread but what disc does the Stillen kit come with?? Just wanted to know because my brother upgraded to the 3.125 (don't know the exact #'s) pulley and is running extremely rich when he goes WOT at high revs. Why would the "stock" disc be so agressive. Wouldn't this cause the car to run very rich with the 'stock' pulley since the ratio is the same?? Which disc should he go with?? Thanx in advance guys.

nismology

iTrader: (8)

bizzump...

BigDogJonx

iTrader: (7)

Tell him to pull out the disc and check the size cause something is wrong if the car is running EXTREMELY rich on a 3.125" and at WOT. How are you measuring how rich he is running? Or better yet, what psi is your Fuel Pressure showing during those times?

BTW here are the disc sizes when he pulls it open to see what he is running.

4:1 = 1.59"
6:1 = 1.85"
8:1 = 2.22"
10:1 = 2.47"

Dixit

nismology

iTrader: (8)

Ummm... He doesn't have a Fuel Pressure Guage. Put it this way, when he looks in the rear-view mirror, he can see a puff of black dark smoke whenever he upshifts and the like. We'll pull out the disc check which one it is. Thanx.

Edit: Is this a DIY job to remove the disc. What tools would I need??

BigDogJonx

iTrader: (7)

To remove the disc is easy, remove the 6 allen head bolts out of the FMU and open it up, then measure the disc size.

Dixit

nismology

iTrader: (8)

Thanx Dixit. We took it out and it's the 8:1 disc. We also checked the pulley and it's the 3.33. I know, that changes things alot but according to what I've read, the 6:1 disc is more suitable for this pulley. Maybe I'm wrong?? I don't know if it makes a difference, but he is a 5th Gen with a V2.

BigDogJonx

iTrader: (7)

6:1 should do. You really need to get a Fuel Pressure gauge and get it dyno tuned for air/fuel ratio. Doing it by ear aint is not accurate, plus there are people that have gained a good 25-50whp on fine tuning with an S-AFC.

Dixit

nismology

iTrader: (8)

What fuel pressure do you think he was seeing with the 8:1 because a concern now is whether or not one of the injectors seized causing a lean condition. The next step is to have an OBD-II diag performed and have a leakdown/compression test. An approximation will do. Thanks for your help.

Mike

thebigsadler

iTrader: (4)

my fuel advice was given to me by an old and wise man, and i will pass it on.

by a cartech

nismology

iTrader: (8)

LOL. I've heard good things about the Cartech, but I just wanted to know which disk my brother should go with cuz stupid Stillen sent the new kits with the 8:1. I guess a 6:1 recalibration is in order. As for my post before this, what kind of fuel pressure would the car see with the 3.33 pulley and 8:1 disk?? Furthermore, what fuel pressure can the stock injectors take without seizing?? BTW, your car is absolutely gorgeous.

Mike

BigDogJonx

iTrader: (7)

Old wise man? Shiet............ Hope that wasnt me

Stillen sends the new kits with 8:1 to stay on the safe side. 3.33 should be alright with an 8:1, if you had an SAFC you could lean out the car where it needs to be done. Like I said, you really need to take it dyno tuned with a Wideband O2 cause doing it by ear aint the best way. Many people have screwed up their cars.

Dixit

IceY2K1

iTrader: (3)

If he has an open atmosphere blow-off valve, then puffs of black smoke are normal on upshifts.

On the shift the blow-off valve releases metered air, but the ECU still dumps in fuel for the released air the engine never sees and you get too much fuel = puff of smoke.

nismology

iTrader: (8)

But that's the thing. He still has the "stock" Bosch unit. I'm thinking the 8:1 is way overkill for the 3.33 pulley. And wouldn't what you said only be the case if the MAF was placed before the blow-off valve?? And it's not only on upshifts. It's whenever he goes WOT. The FMU just needs to be recalibrated and dyno tuned I guess.

Mike

IceY2K1

iTrader: (3)

Yes, on the BOV...wasn't sure what car/setup.

I'll let the SC guys answer the 8:1 question.

IceY2K1

iTrader: (3)

Now that I've thought about it more...I think it's still possible even with the MAF after the BOV. If the throttle-plate closes, the air surges backwards through the MAF before being released out the BOV. Still metered air being vented, right?

Plus, the MAF measures the amount of air by the amount of voltage it takes to keep the hot-wire a constant temperature, so if the air is flowing past the wire in either direction it will be cooled and thus the ECU will add more fuel.

I still think you need a FP gauge(try baggs "Red-neck" FP gauge ) and a dyno to know 100% for sure what's going on.

nismology

iTrader: (8)

Hmm... I never thought about it in that light. I guess it would cause a slighty rich condition, but nowhere as rich as if the MAF was in the intake pipe. You're right about the FP guage and being dyno tuned. I've searched all over this forum and concluded that the 8:1 is overkill for this pulley. If he ever decides to upgrade pulleys we just stick the 8:1 back in. No problem. Thanx for your input.

Mike